Fractures are a common clinical condition. In 1997 in the United States alone, there were approximately eight million fractures. In the same time period there were more than 25 million worldwide. In the treatment of fractures more than 740,000 repair procedures were performed at US hospitals. Of the fracture repair procedures, a total of 9,110 open-reduction without internal fixation procedures were performed and a total of 468,310 open-reduction with internal fixation procedures were performed. Some key statistics that are applicable to the specific scope of the current study are those related to non-unions and malunions. It has been reported that between 2-7% of fractures are nonunions. Many of the nonunion fractures occur in the tibia. The overall rate of delayed union in tibia fractures ranges from 5-61%, and the rate for nonunions in tibial fractures vary from 0-21%.
The number of procedures that could utilize the proposed fracture fixation sleeve of the present invention includes the open-reduction procedures primarily of long bone fractures (477,420 procedures). In particular, the procedures that utilize bone graft or orthobiologic agents (10%) would be applicable (47,720 procedures). Also of note would be the nonunion fractures (14,800 procedures).
One major goal of orthopaedic surgery is to incorporate methods that will stimulate the healing of bone. Many methods of treatment yield successful results, however complications do arise. Bone grafts and synthetic materials are often applied in these circumstances. Basic science has progressed this area of orthopaedics a great deal, however a continued need for quality research and new, useful products exists. The dynamic nature of bone and its ability to repair itself makes this a challenging endeavor in the orthopaedic community.
Bone is a material that is characterized by cells and mineral salts embedded in a fibrous matrix. Each of the base materials of bone supply essential components of the strength which are required to maintain the overall mechanical function of osseous tissue. Among two of the key elemental materials leading to the functional strength of bone are Type I collagen and hydroxyapatite (HAp). The fibrous matrix of bone is comprised primarily of collagen (90%). Type I collagen is required for the tensile strength in bone. Bones are required to maintain a significant amount of tensile strength resistance due to the bending loads that are applied during normal functioning. The strength and rigid nature of bone is due to the mineral component of the material. In bone, the mineral component consists mainly of hydroxyapatite. The combination of the basic substrates of bone leads to a material that can resist and transfer both tensile and compressive loads.
A fracture occurs when the forces that are applied exceed the load bearing capacity of the bone. The result is structural failure. The load applied, the direction of the load, the size and geometry of the bone, and the material properties of the bone are all factors in determining if or when a bone will fracture. Several mechanisms play a role in the healing of a bone after fracture. There are biochemical, biomechanical, cellular, hormonal, and pathological factors that influence the bone healing process.
The healing process of bone resembles the early stages of bone development. The injured area first goes through an inflammatory stage characterized by the migration of cells to the region and followed by an ingrowth of vascular tissue into the affected area. The next phase of fracture healing involves the development of a supportive connective tissue generated by fibroblasts. The connective tissue network supports the vascular growth into the area as healing takes place. Finally, the fracture healing process is completed with the remodeling phase. The goal of the remodeling phase is to return the bone to its original shape, structure, and mechanical strength. The remodeling process is time dependent. It is characterized by a process whereby the bone reacts to the mechanical stress it is subjected to through a dynamic resorption/growth process. As a bone is mechanically loaded, it will respond by building new tissue, realigning the matrix and minerals, and resorption of bone where adequate loading is not present. There are several reasons why fractures fail to heal. Among these are: inadequate immobilization, comminuted and devascularized bone, poor vascularity, infection, prior irradiation, bony defects, systemic factors, reaction to medications, and smoking. The failure of a fracture to heal is considered a non-union or delayed union fracture.
Non-union or delayed-union fractures are among the most difficult to treat. Fractures that do not properly heal resulting in a delayed or nonunion may require several surgeries utilizing a variety of techniques. Surgical methods utilized in the treatment of such fractures include: plating, internal fixation, intramedullary nails, and the use of bone grafting or bone substitute materials. Failure of the surgical methods can result in pseudoarthritis of the fracture site, instability, loss of weight-bearing ability, and painful, device assisted ambulation.
One method that is utilized extensively in the treatment of the specified fractures is the use of bone grafting or the use of bone substitutes. Materials that are used can be either osteogenic, osteoconductive, or osteoinductive. A variety of materials are used, but they can be divided into several specific groups. The generalized categories are autograft, allograft, xenograft, synthetic materials, and various combinations.
Despite many advances in the methods to treat these specified fractures using implanted medical devices including synthetic materials, there are still concerns with the ability of synthetic materials to integrate with the body's tissues. The use of materials produced from the body's own biopolymers can reduce the risk of detrimental effects and increase the body's ability to regenerate itself. Natural biomaterials have been researched, however they have not been shown to demonstrate the required physical properties required for implant systems.